Current Problem
When a JIRA user is created with username: Müller, then, although he can can access most JIRA options BUT he can not access Agile Boards.

Reproduce steps
1. On User Management page, create a JIRA user with below username

Müller

2. Log in jira with this username, then go to Agile -> BoardName
3. JIRA keep loading the board repeatedly.

Cause
The second character, which is Ü is a german character.
Same for ä and ö

Expected Outcome
This user should access Agile Board without any issue.